1. Field of the Invention
The present invention relates to correction of a display variation of a display apparatus having an electroluminescence element in each pixel.
2. Description of the Related Art
Electroluminescence (hereinafter referred to as “EL”) display apparatuses in which an EL element which is a self-emissive element is employed as a display element in each pixel are expected as a flat display apparatus of the next generation, and are being researched and developed.
After an EL panel is created in which an EL element and a thin film transistor (hereinafter referred to as “TFT”) or the like for driving the EL element for each pixel are formed on a substrate such as glass and plastic, the EL display apparatus is subjected to several inspections and is then shipped as a product.
In a current active matrix EL display apparatus having a TFT in each pixel, a brightness unevenness occurs among the EL elements because of display unevenness caused by the TFT, in particular, a variation in the threshold value Vth of the TFT, which is a major cause of reduction in yield. An improvement in the yield of the products is very important, and, thus, reduction in the display defect and display unevenness (display variation) by improving an element design, a material, a manufacturing method, or the like is desired. Attempts have been made, for example, as described in JPA 2005-316408 (hereinafter referred to as “Reference Document 1”), in which, when a display unevenness or the like occurs, the display unevenness is corrected so that the panel is made a non-defective panel.
In the Reference Document 1, the EL panel is caused to emit light, the brightness of each pixel is measured, and a data signal (video signal) to be supplied to the pixel is corrected according to the variation in the brightness. In addition, as another method, a method is proposed in which a circuit which corrects the variation of Vth of an element driving transistor which controls a current to be supplied to the EL element is provided in each pixel.
In a structure in which the EL panel is caused to emit light and an image of the emission is captured with a camera in order to measure the brightness variation as described in the Reference Document 1, when a resolution of the EL panel is increased and a number of pixels in the EL panel is increased, a number of the measurement and correction target becomes large for measuring the brightness variation for each pixel, and, thus, an increase in the resolution of the camera, an increase in capacity of a storage of correction information, etc. is required.
Moreover, even when the circuit element for compensating Vth is not to be incorporated, it is highly desired to correct the display unevenness caused by the variation in Vth of TFTs.